Temperature effect of rare earth-doped TiO₂ electrorheological fluids

Doping of rare earth into anatase TiO₂ has been found to improve the electrorheological (ER) effect of the TiO₂; in this paper we investigate the temperature dependence of the rheological, dielectric and conduction properties of its ER fluids. Typical cerium-doped TiO₂ ER fluid shows the highest shear stress around 80°C, but that of a pure TiO₂ ER fluid decreases with temperature beyond 40°C. The dielectric constant, loss and conductivity of Ce-doped TiO₂ ER fluid increase with temperature, and it exhibits marked dielectric relaxation around 70°C at 1 kHz. However, the dielectric and conduction properties of pure TiO₂ ER fluid is independent of temperature. This remarkable difference in the temperature dependence of the dielectric and conduction properties between doped and pure TiO₂ ER fluids can well explain the different temperature effects of their rheological properties. Furthermore, we preliminarily discuss the above results on the basis of lattice distortion, defects or impurities in TiO₂ originating from the substitution for Ti⁴⁺ by large-radius rare earth ions.